One-Step Surface Wafer Damage Removal for Improved Interface Passivation in Silicon Heterojunction Solar Cells

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Abstract
This work presents an optimisation study of silicon surface preparation for silicon heterojunction solar cells (SHJ) fabricated from surface-damaged wafers, aiming to ensure minimal surface defects and improved passivation at the crystalline silicon-hydrogenated amorphous silicon (c-Si/a-Si:H) interface. KOH etching conditions were optimized to remove diamond‑wire‑saw (DWS) damage on c‑Si while tuning nanoscale faceting for improved interface passivation. Namely, KOH 45% was used to smooth the surface and remove saw damage, while KOH 5% generated approximately 20 nm pyramidal‑like features in a single‑step, IPA‑free process. For the fabrication of SHJ solar cells with an Aluminium Back Surface Field (Al-BSF), intrinsic and n-type doped a-Si:H layers were deposited by plasma-enhanced chemical vapor deposition (PECVD) on the front side of the devices. Two different (i)a-Si:H films, one dense, deposited with 50% hydrogen dilution, (id)a-Si:H, and the other, under-dense, using pure silane gas, (iud)a-Si:H, were used in different solar cells. A relative improvement of 18% in implied PCE (Suns‑Voc) was observed for KOH 5% with dense (id)a‑Si:H versus KOH 45%, which was attributed to the effect of nanoscale faceting created on the c‑Si surface by the 5% KOH treatment.